1. Field of the Invention
The present invention relates generally to the control of a hybrid electric vehicle, and more particularly to a method for controlling a wheel drive system of a hybrid electric vehicle when starting a power source, such as an engine.
2. Background Art
Previously, hybrid electric vehicles used specialized control strategies to start an engine. An example of such a strategy is described in U.S. Pat. No. 6,581,705 assigned to the assignee of the present invention. The method in the aforementioned patent utilizes a complex control strategy that monitors the rotational speeds of an engine and a motor/generator, determines a speed slip error indicative of the “slip” of a disconnect clutch disposed between the engine and the motor/generator, and controls the motive torque provided to the engine by a motor/generator. The engine is considered to be started when the slip speed error and motor/generator torque remain below different calibratable tolerances values for a certain amount of time.
It is desirable to provide a simplified, speed-based control strategy for starting an engine in a hybrid electric vehicle. In addition, it is desirable to provide a control strategy that supports engine startups when the vehicle is not already in motion. Problems associated with the prior art as noted above and other problems are addressed by applicant's invention as summarized below.